The present invention relates to a fuel supply control apparatus for an internal combustion engine which controls the supply quantity of fuel into a combustion chamber of the engine.
Conventionally, as a means for electronically controlling the fuel supply quantity into a combustion chamber of an internal combustion engine on the basis of the state of the engine and the travelling state of the motor vehicle, there is known an apparatus which detects the state of the engine to increase the fuel supply quantity into the combustion chamber when the engine takes a high-load state. For example, the decision as to whether or not the engine takes the high-load state is made on the basis of the degree of the pressure within the intake pipe without using a throttle valve opening sensor. More specifically, a decision level for deciding the high-load state is set on the basis of the speed of the engine so as to be compared with the intake pipe pressure so that the high-load state is determined when the intake pipe pressure exceeds the decision level (for example, as disclosed in the Japanese Patent provisional Publication No. 1-277631). There is a problem which arises with such a technique, however, in that, in the case that the motor vehicle is running at a highland or in other cases, the intake pipe pressure is affected by the atmospheric pressure so that the intake pipe pressure does not become above the decision level irrespective of the engine taking the high-load state, whereby difficulty is encountered to obtain a sufficient output from the engine.
One possible solution is that an atmospheric-pressure sensor is provided to correct the intake pipe pressure on the basis of the detection result of the atmospheric-pressure sensor. However, this technique also provides a problem that the apparatus becomes complicated because of additionally providing a new sensor. Further, as disclosed in the Japanese Patent provisional Publication No. 61-207857, there is known a technique where the gear position of the transmission is detected so that, when the actual engine speed is higher than a predetermined value sit in correspondence with each of the gear positions, the decision is made such that the throttle valve is in the fully opening state, and in this time the detection value of the intake pipe pressure sensor is read as the atmospheric pressure so as to correct the decision level on the basis of the read atmospheric pressure to compare the corrected decision level with the intake pipe pressure to check whether the engine is in the high-load state. However, for example, in the case that the motor vehicle is going down a slope, this technique also has a problem. That is, when the engine speed gradually increases to exceed a predetermined value irrespective of the throttle valve being in the half-opening or slightly opening state, the decision is made in error such that the throttle valve is in the fully opening state, whereby there is the possibility that at this time the intake pipe pressure is read as the atmospheric pressure in accordance with the error decision to make it difficult to accurately decide the high-load state of the engine. Further, in the case that the motor vehicle is going up a slope, there is the possibility that, irrespective of the throttle valve taking the fully opening state, the high-load decision is not made because the engine speed scarcely increases.